Clinical and Experimental Rheumatology 2006; 24: 698-701.
BRIEF PAPER
The serum levels of
resistin in rheumatoid
arthritis patients
K. Migita1,2, Y. Maeda1,
T. Miyashita1,2, H. Kimura2,
M. Nakamura1, H. Ishibashi1,
K. Eguchi3
1
Clinical Research Center and
Department of General Internal Medicine,
NHO Nagasaki Medical Center, Kubara
2-1001-1, Omura 856-8652, Japan;
3
First Department of Internal Medicine,
Nagasaki University School of Medicine
Sakamoto 1-7-1, Nagasaki 852-8501,
Japan.
Kiyoshi Migita, MD; Yumi Maeda, PhD;
Taichiro Miyashita, MD; Hironori Kimura,
MD; Minoru Nakamura, MD; Hiromi
Ishibashi, MD; Katsumi Eguchi, MD.
Please address correspondence to:
Kiyoshi Migita MD, Clinical Research
Center, NHO Nagasaki Medical Center,
Kubara 2-1001-1, Omura 856-8652,
Japan.
E-mail: [email protected]
Received on December 12, 2005; accepted
in revised form on June 15, 2006.
© Copyright CLINICAL AND EXPERIMENTAL RHEUMATOLOGY 2006.
2
Key words: Cytokine, resistin,
rheumatoid arthritis, tumor necrosis
factor-α.
ABSTRACT
Objective. Adipocyte-derived resistin
is a circulating protein implicated in
insulin resistance, but the role of
human resistin is uncertain because it
is produced largely by macrophages.
The aim of this study was to analyze
serum resistin concentrations in
rheumatoid arthritis (RA) patients to
determine the role of resistin in human
inflammatory diseases.
Materials and methods. Resistin concentrations were assessed by ELISA in
serum samples from 42 patients with
RA. Serum samples from 38 healthy
subjects acted as controls. We also
evaluated the circulating levels of
tumor necrosis factor-α (TNF-α) and
disease activity markers in RA patients.
Results. In RA patients, serum resistin
levels were significantly higher than
those in healthy subjects. Serum
resistin levels in RA patients were correlated with the RA disease activity
markers, CRP and ESR. Furthermore,
resistin levels in RA patients were significantly correlated with circulating
levels of TNF-α.
Conclusion. Serum resistin levels were
significantly increased in RA patients
and correlated with inflammatory
markers and TNF-α, suggesting that
resistin may play a role in the rheumatoid inflammatory process.
Introduction
Adipocytes secrete several active molecules such as leptin, adiponectin and
resistin (1).
These substances, collectively known
as adipokines, may function as signaling molecules that influence insulin
sensitivity (2). These products secreted
by adipose tissues also play a role in
inflammation and immune responses
(3). Resistin was initially described as
an adipocyte-derived mediator of
hepatic insulin resistance and is regulated by peroxisome proliferator-activated receptor gamma (4). Initial studies in rodents suggest that resistin is
upregulated in obesity and may be
involved in the development of insulin
resistance (5). Later studies have failed
to confirm this hypothesis and demonstrated reduced resistin expression in
human adipose tissues (6). Although
698
resistin can be detected at very low levels in human adipose tissues, this protein is also detectable in peripheral
blood mononuclear cells suggesting its
possible role in inflammatory processes (7). Therefore, resistin is thought to
be linked to inflammatory diseases as
well as metabolic diseases. Because
inflammatory cytokine production is
involved in the pathogenesis of rheumatoid arthritis (8), we investigated
whether circulating levels of resistin
are elevated in patients with rheumatoid arthritis (RA).
In the present study, we found that
serum levels of resistin were significantly elevated in RA patients compared to those of healthy controls, and
that the levels were correlated with
serum levels of tumor necrosis factor
(TNF)-α in RA patients. Our results
suggest that resistin could be modulated by inflammatory cytokines and may
play a role in the inflammatory process
of RA.
Patients and methods
Patients
Serum samples were collected from 42
RA patients who fulfilled American
College of Rheumatology classification criteria for RA, and who attended
the Rheumatology Clinic of Nagasaki
Medical center. RA patients with metabolic diseases, infections and other
inflammatory diseases were excluded
in this study. The collected samples
were stored at -70ºC until use. Thirty
eight healthy subjects (7 men and 31
women) with a mean body mass index
(BMI) of 20.6 kg/m2 were recruited as
controls for this study (Table I).
Healthy subjects were defined as individuals with a blood pressure of less
than 140/90 mmHg, normal renal and
liver function, a fasting plasma glucose
level of less than 90 mg/dl and a postprandial 2-hour plasma glucose level of
less than 140 mg/dl. No healthy subjects of them were suffering from other
diseases. Informed consent was
obtained from each individual.
Laboratory analysis
Serum levels of C-reactive protein
(CRP) were measured by standard
nephelometry, with established normal
The serum levels of resistin in RA patients / K. Migita et al.
BRIEF PAPER
Table I. Clinical characteristics of RA patients.
Age, years (range)
Gender, male / female
Disease duration, years (range)
DAS28 (CRP)
BMI
Treatment
Steroid
Methotrexate
Other DMARDs
RA patients (n = 42)
healthy controls (n = 38)
53.3 ± 15.4 (31-82)
10/32
7.0 ± 6.5 (1-40)
3.6 ± 1.0
22.5 ± 4.4
45.5 ± 13.3 (28-76)
7/31
NA
NA
20.6 ± 2.3
30/42
9/42
35/42
NA: Not analyzed; DMARDs: disease-modifying anti-rheumatic drugs.
range 0-3 mg/l. Erythrocyte sedimentation rates (ESR) was measured by the
Westgren method with the normal
range defined as 0-14 mm/hr. Total
cholesterol, triglyceride, and LDL cholesterol levels were measured in serum
automated enzymatic procedures
(TBA200FR, Toshiba, Japan). HbA1c
was measured by HA-8160 analyzer
(Arklay, Japan).
ELISA
Serum levels of TNF-α were determined by enzyme-link immunosorbent
assay (ELISA) kit (R&D Systems,
Minneapolis, MN, USA) following to
the manufacturer’s instructions. Serum
levels of resistin were determined by
sandwich ELISA (Bio Vendor, Brno,
Czech Republic).
Statistical methods
The levels of continuous variable were
expressed as mean ± SEM. Differences
between groups were calculated using
the Mann-Whitney U test. The level of
correlation between resistin and biochemical characteristics was assessed by
Pearson’s correlation test. P values of <
0.05 were considered to be significant.
All statistical analyses were performed
with version 6.0 of StatView for Windows (SAS Institute Inc, Cary, NC, USA)
Results
Clinical data of the RA patients at
presentation
Table I presents the clinical data of the
RA patients and control subjects who
were all of similar sex, height, body
weight, BMI and age.
Fig. 1. Serum resistin levels in RA patients and healthy subjects.
The box contains the values between the 25th and 75th percentiles and the horizontal line is the median.
The error bars stretch the 10th to 90th percentiles.
699
Increased levels of resistin in the blood
of RA patients
As shown in Figure 1, serum resistin
levels were found to be significantly
higher in RA patients compared to
those in control subjects (RA, 6.72 ±
4.59ng/ml; control subjects, 3.15 ±
1.66ng/ml; P = 0.0005). The correlations between resistin and metabolic or
inflammatory markers in RA patients
are listed in Table II. There was a significant positive correlation between
resistin and inflammatory markers
(CRP, ESR). On the other hand, there
was no correlation between resistin and
BMI or dose of prednisolone (Table II).
Correlations between serum levels of
resistin and cytokines in RA patients
We sought to evaluate the relationship
between resistin and an inflammatory
cytokine, TNF-α, which is thought to
be key pathogenic factors in RA. As
reported previously (8), serum levels of
TNF-α (Fig. 2A) were significantly
higher in RA patients than in healthy
subjects. The correlation between
serum levels of resistin and circulating
TNF-α reached statistically significant
levels (Fig. 2B).
Discussion
Resistin (FIZZ3 / ADSF) is an adipocyte-derived peptide first identified
during a search for targets of thiazolidinediones (4). Steppan et al. (5)
reported that serum concentrations of
resistin were markedly increased in
obese mice and decreased by treatment
with thiazolidinediones. Therefore, resistin has been thought to be linked in
obesity with insulin resistance and diabetes in a mouse model (9). However,
in humans, the expression of resistin in
adipocytes is very low compared with
that in rodents, but resistin mRNA is
detectable in circulating mononuclear
cells (7), which suggests that human
resistin plays a role in inflammatory
conditions.
The present study showed significantly
increased resistin levels in the sera of
RA patients compared with healthy
subjects. Furthermore, the increased
serum levels of resistin correlated with
CRP or ESR in RA patients. This positive correlation between resistin and
The serum levels of resistin in RA patients / K. Migita et al.
BRIEF PAPER
inflammatory markers in RA patients
suggests that the increased resistin values found in RA patients could be
linked to the rheumatoid inflammation. Our data differ from those presented in a recent study by Bokarewa
et al. (10) in which blood resistin levels were not significantly different
between RA patients and controls.
Although the reason for this discrepancy is unknown, blood resistin levels
were relatively lower in our control
subjects than in the controls in Bokarewa’s study. Serum resistin levels in our
control subjects, however, were quite
similar to those reported data by Heilfronn (11), in whose study circulating
resistin levels of non-obese and nondiabetic healthy subjects were analyzed by the same ELISA kit used in
the present study.
There was a significant positive correlation between serum resistin and TNFα in our study. Lehrke et al. showed
that lipopolysaccharide (LPS), a potent
inflammatory stimulant, increases
resistin production by inducing the
secretion of the inflammatory cytokine
TNF-α in humans (12). These data suggest that hyperresistinemia could be
associated with systemic inflammation
via TNF-α, as well as metabolic disorders such as obesity or insulin resistance. The increased circulating resistin
levels of the RA patients in the present
study could have been induced by
rheumatoid inflammation via the inflammatory cytokine, TNF-α. Bokarewa
et al. recently demonstrated that resistin displays proinflammatory properties by strongly up-regulating IL-6
and TNF-α from human PBMCs (10).
Alternatively, the positive correlation
between serum levels of resistin and
TNF-α in RA patients suggests that
resistin partly contributes to the inflammatory cytokine production in these
patients.
More recently, Otero et al. reported that
there was no significant difference in
serum resistin levels between RA
patients and healthy subjects (13). The
reason for this discrepancy could be
differential characteristic of the investigated RA patients. In our study, no RA
patient was treated by TNF-blocker. In
contrast, 26% of RA patients were treat-
Table II. Correlations among resistin and metabolic or inflammatory markers in RA
patients.
Resistin
BMI
Total cholesterol
Triglycerides
ESR
CRP
Dose of PSL
Resistin
BMI
-0.056
-0.027
0.048
0.430**
0.390*
0.039
0.425**
0.430**
-0.226
-0.145
0.157
Total
Triglycerides
cholesterol
0.445**
-0.021
-0.138
0.079
-0.079
0.077
0.441*
ESR
0.656**
0.540**
CRP
0.673**
BMI: body mass index; ESR: erythrocyte sedimentation rate; CRP: C-reactive protein; PSL: prednisolone; *P< 0.05; **P < 0.01.
Fig. 2A Serum TNF-α levels in RA patients and healthy subjects.
The box contains the values between the 25th and 75th percentiles and the horizontal line is the median.
The error bars stretch the 10th to 90th percentiles.
Fig. 2B Correlation between
serum levels of resistin and
TNF-α in RA patients.
TNF-α: tumor necrosis factor-α.
ed by TNF antagonists, and mean CRP
was controlled to relatively low levels
in their study (mean CRP = 0.61 ±
0.19mg/dl; vs. our RA patients = 2.47 ±
0.79mg/dl). Recent report indicated that
hyperresistinemia is linked with eleva-
700
tion of TNF-α in a human study (12).
Therefore, it is possible that serum
resisting levels could be influenced by
RA disease activity in RA patients.
RA patients appear to have a higher
risk of cardiovascular disease (CVD)
The serum levels of resistin in RA patients / K. Migita et al.
and mortality (14). Previous evidence
supporting an inflammatory basis for
atherosclerosis suggests a link between
rheumatoid inflammation and the risk
of CVD (15). Recent study indicated
that circulating resistin levels are correlated with vascular inflammatory markers and coronary atherosclerosis in
humans (16). These findings suggest
that in addition to inflammatory cytokines, resistin may also be involved in
the inflammation-based etiology of
atherosclerosis in RA.
In conclusion, our study demonstrates a
significant increase in circulating
resistin levels in patients with RA compared with healthy controls. These
increased levels of resistin may be
linked with the chronic inflammation
of RA patients, and resistin is a candidate for inflammatory cytokines contributing to the rheumatoid inflammatory process.
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